Study on the Effects of the Types and Addition Time of Chemical Admixtures on Cement Performance

Abstract

The effects of single admixture and combined admixture of Naphthalene Superplasticizer (NFS), Polycarboxylate Superplasticizer (PCC) and Li2CO3 and the addition time of superplasticizer on the fluidity, strength and adsorption capacity and other properties of cement paste are studied in this paper. NFS and PCC can significantly enhance the fluidity of cement paste; the greater the dosage of chemical admixture, the longer the initial setting time of cement; the suitable dosage of NFS is 0.4% -0.6%; the overall fluidity is the best, when the content of Li2CO3 is 0.01%. The combined admixture of PCC and Li2CO3 has little effect on the fluidity of cement paste. The higher the content of Li2CO3, the larger the adsorption capacity of cement particles to NFS, while the content of Li2CO3 basically does not affect the adsorption capacity of cement to PCC, indicating that Li2CO3 has the auxiliary water reducing effect, which can enhance the fluidity of cement paste. With a combined admixture of NFS and Li2CO3, Li2CO3 will have a great influence on the setting time of cement, and when the content of Li2CO3 is 0.35%, the initial setting time of cement is reduced by about 85.9% and the final setting time is reduced about 82.2%. The cement adsorption capacity of cement drops sharply after adding NFS and PCC 5-10 min after cement hydration. After 10 min, superplasticizer is added, and the declining tendency of cement adsorption capacity gradually becomes gentle. When the content of PCC increases from 0.4% to 0.6% and the content of NFS increases from 0.6% to 1.0%, the electronegativity of the surface of the cement shows an overall increasing trend, but when the superplasticizer is added to the cement 5-10min after hydration, the electronegativity is gradually reduced.